Method of operating jet propulsion motors



Patented July 14, 1953 METHOD OF OPERATING JET PROPULSION MOTORS Thomas F. Doumani, Los Angelcs, and Clarence S. Coe, Long Beach, Calif., assignors to Union Oil Company of California, Los Angeles, Calif., a corporation of California No brawing. Application J une 6, 1944,

Serial N0. 539,030

a jet ornozzle, of the relatively large volume of products resulting from the combustion of a fuel by means of an oxidizing agent. The jet may be exhausted into the open air as in the rocket type of motor, or it may be trained on a movable piece of machinery such as the blades of a fan as in the turbine type of motor.

The primary requisites of auxiliary jet-propulsion motors such as described above, are simplicity of fabrication and efiiciency of operation. The motors should be light in weight, small in size, and simple to construct and operate; and the propellants should be safe to handle, stable in storage, should ignite readily and positively,

and burn rapidly and smoothly, with a maximum 4 Claims. (Cl. 6035.6)

volume of products of combustion. It is an obsured with nitrogen to a pressure of about 1,500

pounds per square inch. The pressuring may be accomplished by release of nitrogen or other inert gas contained in a second tank under high pressure, through suitable lines and a'pressure reducing control valve. The methyl nitrite may then be released from the fuel tank and fed through suitable lines and control valves to a combustion chamber equipped with an igniting device, such as a spark plug, and allowed to burn or decompose in the absence of any added oxidizer.

As an example of the operation of a similar motor in which a separate fuel and oxidizer are employed, a fuel may be prepared by blending about 10% by weight of isopropyl nitrite in about 90% of a paraffinic'crude gasoline fraction, the gasoline fraction having a boiling range of about 100 F. to 400 F. and containing less than about 10% of aromatic type hydrocarbons. This fuel may be charged into one feed tank of a jetpropulsion motor and pressured with nitrogen as above. A second feed tank may be charged with fuming nitric acid and similarly pressured with nitrogen. The fuel and the nitric acid oxidizer may then be released from the fuel tanks and fed to'a combustion chamber where they are allowed to react. This reaction is an oxidation reaction or combustion and the hot gaseous products of the combustion are'utilized as above to provide the driving force. Therates of introduction 'into the combustion chamber may be about two and one-half pounds and three and one 'half pounds for the fuel and oxidizer, respectively, for a combustion chamber of about the above size. The effect of the isopropyl nitrite in the above fuel is to lower the ignition temperature and to make the burning smooth and non-explosive, thus providing a smooth thrust during the entire period of operation rather than a single explosion or a series of explosive bursts. similar effects are obtained with the other fuels or additives of this invention.

It is clear that the invention is not limited to the particular conditions of the above examples, since different pressures, up to several thousand pounds, different rates of introduction of propellants, generally increasing with the pressure and the size of the motor, and different sizes and styles of equipment may be employed, some of which are referred tobelow. The propellants of this invention are particularly effective in any such jet-propulsion motor, to increase the certainty, the smoothness, and the efiiciency of the combustion. Regarding the methyl nitrite of this invention it may be noted that this material is a gas at ordinary temperatures, but is readily liquefied, the liquid having a vapor pressure at about 40 C. of about pounds per square inch gage. Its heat of combustion at 25 C. in calories per mol is over 180,000 and its heat of decomposition to form carbon dioxide, water, carbon and nitrogen is 99 calories per mol. These show that it is especially valuable as a fuel or as a monopropellant, the term monopropellant as used herein referring to a propellant which is a single material rather than a mixture of a fuel and an oxidizer. Methyl nitrite is very easily prepared by the reaction of methanol and sodium nitrite in the presence of sulfuric acid. Homologs of methyl nitrite containing less than about four carbon atoms, such as ethyl nitrite and propyl nitrite may also be used as monopropellants, but when higher homologs containing more than about four carbon atoms are employed, such as octyl nitrite, benzyl nitrite, phenyl nitrite, cyclohexyl nitrite, and the like, it is preferred that some oxidizer be employed also. These materials may be used without dilution as straight fuels, or they may be employed as additi'ves for hydrocarbon fuels, those homologs con- 3 taining less than about four carbon atoms being preferred for the latter use. The nitrites, especially methyl nitrite, are preferred but the nitrates are also very. valuable. The nitrates, especially the lower ones, containing less than about four carbon atoms, such as methyl, ethyl and propyl may also be employed as monopropellants since they have an even larger proportion of oxygen than do the nitrites. For use with oxidizers the nitrates and nitrites which contain more than about four carbon atoms are preferred, especially those having between about six and about sixteen carbon atoms. The organic radicals may be paraffinic, naphthenic, aromatic or olefinic in character, as indicated. above.

Although only the mono nitrites and nitrates have been specifically discussed above, the nitrates and nitrites of this invention also include those compounds containing more than one such polar group in the molecule, such as the dinitrites, dinitrates, nitrite-nitrates, trinitrites and the like. A with the mono substituted compounds, those compounds which contain fewerthan about 4 carbon atoms foreach polar group (or each nitrogenatom) are preferred as mono-propellants or as additives for hydrocarbon fuels, while the higher homologs are preferred as straight fuels. Examples of these material are: cyclohexane-l, l-dinitrate; benzene-1, Z-dinitrite; isobutane nitrite-nitrates; and ethylene glycol dinitrate.

Whcre cxidizers are employed with the above fuels these oxidizers may be nitric acid, oxygen, and nitrous oxide (these three being preferred) or air, ozone, hydroperoxides, metal peroxides, metal manganates, permanganates, chlorates, perchlorates, hypochlorites, persulfateschromites, chromates, bichroin'ates and the like as well as sulfur, the halogens such as fluorine, chlorine, bromine and iodine and their compounds with oxygen, nitrogen and sulfur. The nitric acid is preferably fuming nitric acid containing less than about 5% by Weight of water. White fuming nitric acid containing-less than about of water and substantially no nitrogen dioxide is very suitable and red fuming nitric acid containing up to about 20 by weight of nitrogen dioxide and less than 5% of water is also excellent, although as indicated fuming nitric acid of greater than 95% concen-'- tration is preferred. Any nitric acid having a concentration greater than about 80% may be employed. Liquid nitrogen dioxide may also be employed as Well as other oxides of nitrogen.

Where both the fuel and the oxidizer are fluids, that is, liquids or gases or stable suspensions of solids in liquids, or gases, the method of opera tion described in the specific example may be followed, that is the fuel and oxidizer may be kept in separate compartments until the time of combustion and pressured with a piston gas, such as nitrogen or other inert gas, to force them into the combustion chamber. The combustion chamber may be provided with an igniting device such as a spark plug or a detonating device where necessary, although in certain instances the contact of the fuel with the oxidizer produces spontaneous combustion; Where the fuel is a monopropellant only one storage chamber is necessary and an igniting device must always be employed. .Where both the fuel and the oxidizer are non-fluids, that is, are solids which are not readily transferred from the storage compartment to the combustion chamber, and the mixture of' the fuel and the oxidizer will not spontaneously ignite under storage conditions, the fuel and the oxidizer may be blended or intimately mixed and positioned in the combustion chamber itself in such a position that there is no danger of its obstructin the jet.

Thus, a mixture of asphalt and potassium perchlorate, for example, may be heated sufiiciently to allow it to be poured into the combustion chamber so that it will solidify at the opposite end of the combustion chamber from the jet. It is desirable that when such a mixture is burned it will burn smoothly at the surface of the charge and not burn in a series of explosions. The additives of this invention aid materially in making the combustion of fuel more smooth and in permitting ignition at lower temperatures. Where either the fuel or the oxidizer is a solid and the other component'of the propellant is a fluid the solid material may be positioned in the combustion chamber as described above and the fluid material charged to the combustion chamber as described previously. The proportion of the oxidizer, compared to the fuel in'the propellant employed isv preferably somewhat less than the amount thecretically required for complete com- 'bustion. Generally, proportions between about 50% and about oxidizer'by weight are satisfactory-,although higher or lower proportions may be necessary in some instances.

Modifications of thi invention which would occur to one skilled in the art are to be included in the 1 invention as defined in the followin claims.

We claim:

, 1. In a method of-operating a jet-propulsion I bon atoms for each nitrogen atom, and igniting the fuel therein.

2. In a method of operating a jet propulsion motor, wherein a fuel is burned in a combustion chamber, and the products of combustion are allowed to escape through a jet, thereby producing a driving force, the improvement which comprises injecting into the chamber a fuel consisting essentially of an organic nitrite having not more than four carbon atoms'for each nitrogen atom, and igniting the fuel therein.

3. A method according to claim 2 in which the organic nitrite is methyl nitrite.

4. A method according to claim 1 in which the nitrogen and oxygen containing organic compound is an organic nitrate.

THOMAS F. DOUMANI. CLARENCE S. COE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,103,503 I Goddard July 14, 1914 1,597,343 Chandler Aug. 24, 1926 1,611,353 Lepinte Dec. 21, 1926 1,820,983 Loomis Sept. 1, 1931 2,033,877 Burk Mar. 10, 1936 2,065,588 Howes Dec. 29, 1936' 2,128,987 Christensen Sept. 6, 1938 2,169,186 Shoemaker et al Aug. 8, 1939 2,214,059 Lieber et a1 Sept. 10, 1940 (Other references on following page) Number 5 UNITED STATES PATENTS Name Date Goddard Oct. 8, 1940 Boyd Nov. 26, 1940 Vanderbilt May 13, 1941 Cloud Apr. 21, 1942 Miller et a1 Apr. 6, 1943 Kass July 20, 1943 Crandall et al. Sept. 7, 1943 Seger et al Aug. 8,1944 Noland et a1 Feb. 27, 1945 McCracken Oct. 23, 1945 Malina et a1 May 14, 1946 Number Number 6 Name Date Zwicky et a l Jan. 6, 1948 Miller Aug. 1'7, 1948 FOREIGN PATENTS Country Date Great Britain Jan. 18, 1937 OTHER REFERENCES American Interplanetary Society Bulletin No. 16, February 1932. Report by Lemkin, pp. 8-10. Chemistry of Powder and Explosive by Davis, published by John Wiley, 1943, vol. II, page 193. 

1. IN A METHOD OF OPERATING A JET-PROPULSION MOTOR, WHEREIN A FUEL IS BURNED IN A COMBUSTION CHAMBER IN THE ABSENCE OF SEPARATE OXIDIZER, AND THE PRODUCTS OF COMBINATION ARE ALLOWED TO ESCAPE THROUGH A JET, THEREBY PRODUCING A DRIVING FORCE, THE IMPROVEMENT WHICH COMPRISES INJECTING INTO THE CHAMBER A FUEL CONSISTING ESSENTIALLY OF A NITROGEN AND OXYGEN CONTAINING ORGANIC COMPOUND OF THE CLASS CONSISTING OF ORGANIC NITRITES AND NITRATES CONTAINING NOT MORE THAN FOUR CARBON ATOMS FOR EACH NITROGEN ATOM, AND IGNITING THE FUEL THEREIN. 